Thanks for the ideas but I have worked out another solution which works ...
Basically Josh was correct it was dependencies - when you install IIS from the WinXPSP2 Add/Remove progs applet it should set up the dependencies so that "World Wide Web Publishing" depends on IIS and RPC being present. When I checked the registry settings it turned out that RPC was not listed as a dependency. I have added it and now I get no error on startup.
I had never found these settings before but it was a useful investigation searching for and modifying the dependencies - whic I will not for future reference:
To get the service name go the Administrator Tools > Services applet and double click the service you are interested. The short name for the service is given at the top:
Check out the Dependencies tab:
and then open the properites for the dependency services and note their short names.
Now go to REGEDIT (take extreme care - bad registry editing can destroy your installation!) and find:
replacing ... witht he short service name for the service you are checking ... in my case this was:
One of the values should be called "DependOnService" and should have type REG_MULTI_SZ (if there are dependencies and this value does not exist create it).
Double click "DependOnService" the dependiency servces should be listed one per line (in my case RpcSs was not listed). If any are not present you can add them here. Click OK and close REGEDIT - restart and the dependencies should be fixed.
I am still getting the odd minor glitch on startup with other processes - but they are now rare occurences.
On thing I have noticed is that my network connection now starts and initialises much earlier in the boot process which means apps like IM are logging in more easily whereas before they timed out waiting for the network connection to initialise.